Methods and apparatus for acknowledgment of multi-user uplink wireless transmissions

ABSTRACT

Methods and apparatus for acknowledgment of multiple user uplink are provided. In one aspect, a method of wireless communication includes receiving a first wireless message from a first station at least partially concurrently with receiving a second wireless message from a second station, generating a first acknowledgment message in response to receiving the first wireless message, generating a second acknowledgement message in response to receiving the second wireless message, and transmitting the first acknowledgment message to the first station at least partially concurrently with transmitting the second acknowledgement message to the second station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/871,269 filed Aug. 28, 2013, and entitled “METHODS AND APPARATUS FORMULTIPLE USER UPLINK.” The content of this prior application isconsidered part of this application, and is hereby incorporated byreference in its entirety.

FIELD

Certain aspects of the present disclosure generally relate to wirelesscommunications, and more particularly, to methods and apparatus formultiple user uplink communication in a wireless network.

BACKGROUND

In many telecommunication systems, communications networks are used toexchange messages among several interacting spatially-separated devices.Networks may be classified according to geographic scope, which couldbe, for example, a metropolitan area, a local area, or a personal area.Such networks may be designated respectively as a wide area network(WAN), metropolitan area network (MAN), local area network (LAN), orpersonal area network (PAN). Networks also differ according to theswitching/routing technique used to interconnect the various networknodes and devices (e.g., circuit switching vs. packet switching), thetype of physical media employed for transmission (e.g., wired vs.wireless), and the set of communication protocols used (e.g., Internetprotocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.).

Wireless networks are often preferred when the network elements aremobile and thus have dynamic connectivity needs, or if the networkarchitecture is formed in an ad hoc, rather than fixed, topology.Wireless networks employ intangible physical media in an unguidedpropagation mode using electromagnetic waves in the radio, microwave,infrared, optical, etc. frequency bands. Wireless networksadvantageously facilitate user mobility and rapid field deployment whencompared to fixed wired networks.

In order to address the issue of increasing bandwidth requirements thatare demanded for wireless communications systems, different schemes arebeing developed to allow multiple user terminals to communicate with asingle access point by sharing the channel resources while achievinghigh data throughputs. With limited communication resources, it isdesirable to reduce the amount of traffic passing between the accesspoint and the multiple terminals. For example, when multiple terminalssend uplink communications to the access point, it is desirable tominimize the amount of traffic to complete the uplink of alltransmissions. Thus, there is a need for an improved protocol for uplinktransmissions from multiple terminals.

SUMMARY

Various implementations of systems, methods and devices within the scopeof the appended claims each have several aspects, no single one of whichis solely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

One aspect disclosed is a method of wireless communication. The methodincludes receiving a first wireless message from a first station atleast partially concurrently with receiving a second wireless messagefrom a second station, generating a first acknowledgment message inresponse to receiving the first wireless message, generating a secondacknowledgement message in response to receiving the second wirelessmessage; and transmitting the first acknowledgment message to the firststation at least partially concurrently with transmitting the secondacknowledgement message to the second station.

In some aspects, the first acknowledgment message is a blockacknowledgment and the second acknowledgment message is anacknowledgment of a single frame. In some aspects, the method furtherincludes receiving a third wireless message from the first station, thethird wireless message indicating an acknowledgment policy for the firststation; and transmitting the first acknowledgment message based on theacknowledgment policy for the first station. In some aspects, the methodalso includes determining the first wireless station requests immediateblock acknowledgements based on the third wireless message; andtransmitting the first acknowledgment message based on the determining.

In some aspects, the method also includes receiving a third wirelessmessage from a third station at least partially concurrently with thefirst wireless message and the second wireless message, receiving afourth wireless message from the third station indicating the thirdstation requests delayed block acknowledgments; and transmitting a thirdacknowledgment message to the third station after completion of thetransmissions of the first and second wireless messages based on thefourth wireless message.

In some aspects, the method also includes receiving the first wirelessmessage over a first spatial stream, receiving the second wirelessmessage over a second spatial stream, determining a third spatial streambased on the first spatial stream, determining a fourth spatial streambased on the second spatial stream, transmitting the firstacknowledgment message over the third spatial stream, and transmittingthe second acknowledgment message over the fourth spatial stream.

In some aspects, the method also includes receiving the first wirelessmessage over a first frequency, receiving the second wireless messageover a second frequency, determining a third frequency based on thefirst frequency, determining a fourth frequency based on the secondfrequency; and transmitting the first acknowledgment message over thethird frequency; and transmitting the second acknowledgment message overthe fourth frequency.

In some aspects, the method also includes generating a clear to transmitmessage, the clear to transmit message indicating a third station haspermission to transmit a third wireless message, the clear to transmitmessage further indicating a time when an acknowledgment for the thirdwireless message will be transmitted; and transmitting the clear totransmit message to the third station; and transmitting anacknowledgment to the third wireless message at the indicated time.

Another aspect disclosed is an apparatus for wireless communication. Theapparatus includes a receiver configured to receive a first wirelessmessage from a first station at least partially concurrently withreceiving a second wireless message from a second station, a processorconfigured to generate a first acknowledgment message in response toreceiving the first wireless message, and generate a secondacknowledgement message in response to receiving the second wirelessmessage; and a transmitter configured to transmit the firstacknowledgment message to the first station at least partiallyconcurrently with transmitting the second acknowledgement message to thesecond station.

In some aspects, the apparatus also includes receive a third wirelessmessage from the first station, the third wireless message indicating anacknowledgment policy for the first station; and transmitting the firstacknowledgment message based on the acknowledgment policy for the firststation. In some aspects of the apparatus the processor is furtherconfigured to determine the first wireless station requests immediateblock acknowledgements based on the third wireless message, and thetransmitter is further configured to transmit the first acknowledgmentmessage based on the determining.

In some aspects of the apparatus, the receiver is further configured toreceive a third wireless message from a third station at least partiallyconcurrently with the first wireless message and the second wirelessmessage, receive a fourth wireless message from the third stationindicating the third station requests delayed block acknowledgments; andthe transmitter is further configured to transmit a third acknowledgmentmessage to the third station after completion of the transmissions ofthe first and second wireless messages based on the fourth wirelessmessage.

In some aspects of the apparatus, the receiver is further configured toreceive the first wireless message over a first spatial stream andreceive the second wireless message over a second spatial stream, andwherein the processor is further configured to determine a thirdfrequency based on the first spatial stream and determine a fourthfrequency based on the second spatial stream; and the transmitter isfurther configured to transmit the first acknowledgment message over thethird spatial stream and transmit the second acknowledgment message overthe fourth spatial stream.

In some aspects of the apparatus, the receiver is further configured toreceive the first wireless message over a first frequency and receivethe second wireless message over a second frequency, and wherein theprocessor is further configured to determine a third frequency based onthe first frequency and determine a fourth frequency based on the secondfrequency; and the transmitter is further configured to transmit thefirst acknowledgment message over the third frequency and transmit thesecond acknowledgment message over the fourth frequency.

In some aspects of the apparatus, the processor is further configured togenerate a clear to transmit message, the clear to transmit messageindicating a third station has permission to transmit a third wirelessmessage, the clear to transmit message further indicating a time when anacknowledgment for the third wireless message will be transmitted; andthe transmitter is further configured to transmit the clear to transmitmessage to the third station; and transmit an acknowledgment to thethird wireless message at the indicated time.

Another aspect disclosed is a method of wireless communication. Themethod includes transmitting, via a first wireless device, a firstwireless message to a second wireless device at least partiallyconcurrently with a transmission by a third wireless device of a secondwireless message to the second wireless device; and receiving anacknowledgment message for the first wireless message at least partiallyconcurrently with receiving at least a portion of a secondacknowledgment message for the second wireless message.

In some aspects, the method further includes generating a third wirelessmessage, the wireless message indicating an acknowledgment policy foracknowledging the first wireless message; and transmitting the thirdwireless message to the second wireless device.

Some aspects of the method further include generating the third wirelessmessage to indicate an acknowledgment policy of immediate blockacknowledgment or acknowledgment of a single frame. In some aspects, themethod further includes receiving a clear to transmit message from thesecond wireless device, decoding the clear to transmit message todetermine a time to transmit the first wireless message; andtransmitting the first wireless message at the determined time.

Some aspects of the method include transmitting, via the first wirelessdevice, an acknowledgment policy message indicating delayed blockacknowledgments are requested, transmitting, via the first wirelessdevice, a third wireless message to the second wireless device at leastpartially currently with a transmission by a fourth wireless device of afourth wireless message transmitted to the second wireless device; andtransmitting a block acknowledgment request message to the secondwireless device, the block acknowledgment request message requestingacknowledgment of the third wireless message; and receiving a blockacknowledgment message for the third wireless message from the secondwireless device.

Some aspects of the method also include receiving the acknowledgment forthe first wireless message over a first spatial stream and receiving thesecond acknowledgment message over a second spatial stream. In someaspects, the method also includes receiving the acknowledgment for thefirst acknowledgment message over a first frequency and receiving thesecond acknowledgment message over a second frequency.

Another aspect disclosed is an apparatus for wireless communication. Theapparatus includes a transmitter configured to transmit a first wirelessmessage to a second wireless device at least partially concurrently witha transmission by a third wireless device of a second wireless messageto the second wireless device; and a receiver configured to receive anacknowledgment message for the first wireless message at least partiallyconcurrently with receiving at least a portion of a secondacknowledgment message for the second wireless message.

In some aspects, the apparatus also includes a processor configured togenerate a third wireless message, the wireless message indicating anacknowledgment policy for acknowledging the first wireless message,wherein the transmitter is further configured to transmit the thirdwireless message to the second wireless device. In some aspects of theapparatus, the processor is further configured to generate the thirdwireless message to indicate an acknowledgment policy of immediate blockacknowledgment or acknowledgment of a single frame.

In some aspects of the apparatus, the receiver is further configured toreceive a clear to transmit message from the second wireless device, andwherein the processor is further configured to decode the clear totransmit message to determine a time to transmit the first wirelessmessage, and the transmitter is further configured to transmit the firstwireless message at the determined time.

In some aspects of the apparatus, the transmitter is further configuredto transmit an acknowledgment policy message indicating delayed blockacknowledgments are requested, transmit a third wireless message to thesecond wireless device at least partially currently with a transmissionby a fourth wireless device of a fourth wireless message transmitted tothe second wireless device, transmit a block acknowledgment requestmessage to the second wireless device, the block acknowledgment requestmessage requesting acknowledgment of the third wireless message, and thereceiver is further configured to receive a block acknowledgment messagefor the third wireless message from the second wireless device.

In some aspects of the apparatus, the receiver is further configured toreceive the acknowledgment for the first wireless message over a firstspatial stream and receive the second acknowledgment message over asecond spatial stream. In some aspects of the apparatus, the receiver isfurther configured to receive the acknowledgment for the firstacknowledgment message over a first frequency and receive the secondacknowledgment message over a second frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system with access points and user terminals.

FIG. 2 illustrates a block diagram of the access point and two userterminals in a MIMO system.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice that may be employed within a wireless communication system.

FIG. 4 shows a time diagram of an example frame exchange of an uplink(UL) MU-MIMO communication.

FIG. 5 shows a time diagram of another example frame exchange of anUL-MU-MIMO communication.

FIG. 6 shows a time diagram of another example frame exchange of anUL-MU-MIMO communication.

FIG. 7 shows a time diagram of another example frame exchange of anUL-MU-MIMO communication.

FIG. 8 is a message timing diagram of one embodiment of multi-useruplink communication.

FIG. 9 shows a diagram of one embodiment of a request to transmit (RTX)frame.

FIG. 10 shows a diagram of one embodiment of a clear to transmit (CTX)frame.

FIG. 11 shows a variety of message exchanges that demonstrateacknowledgment methods that may be employed by one or more of thedisclosed embodiments.

FIG. 12 is a message flow diagram illustrating a uplink multi usertransmission.

FIG. 13 is a method of acknowledging a wireless message.

FIG. 14 is a flowchart of a method of receiving acknowledgment of awireless message.

DETAILED DESCRIPTION

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. The teachings disclosure may, however, be embodied in manydifferent forms and should not be construed as limited to any specificstructure or function presented throughout this disclosure. Rather,these aspects are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. Based on the teachings herein one skilled in the artshould appreciate that the scope of the disclosure is intended to coverany aspect of the novel systems, apparatuses, and methods disclosedherein, whether implemented independently of or combined with any otheraspect of the invention. For example, an apparatus may be implemented ora method may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Wireless network technologies may include various types of wirelesslocal area networks (WLANs). A WLAN may be used to interconnect nearbydevices together, employing widely used networking protocols. Thevarious aspects described herein may apply to any communicationstandard, such as Wi-Fi or, more generally, any member of the IEEE802.11 family of wireless protocols.

In some aspects, wireless signals may be transmitted according to ahigh-efficiency 802.11 protocol using orthogonal frequency-divisionmultiplexing (OFDM), direct-sequence spread spectrum (DSSS)communications, a combination of OFDM and DSSS communications, or otherschemes. Implementations of the high-efficiency 802.11 protocol may beused for Internet access, sensors, metering, smart grid networks, orother wireless applications. Advantageously, aspects of certain devicesimplementing this particular wireless protocol may consume less powerthan devices implementing other wireless protocols, may be used totransmit wireless signals across short distances, and/or may be able totransmit signals less likely to be blocked by objects, such as humans.

In some implementations, a WLAN includes various devices which are thecomponents that access the wireless network. For example, there may betwo types of devices: access points (“APs”) and clients (also referredto as stations, or “STAs”). In general, an AP serves as a hub or basestation for the WLAN and an STA serves as a user of the WLAN. Forexample, a STA may be a laptop computer, a personal digital assistant(PDA), a mobile phone, etc. In an example, an STA connects to an AP viaa Wi-Fi (e.g., IEEE 802.11 protocol such as 802.11ah) compliant wirelesslink to obtain general connectivity to the Internet or to other widearea networks. In some implementations an STA may also be used as an AP.

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Spatial Division Multiple Access (SDMA),Time Division Multiple Access (TDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) systems, and so forth. An SDMA system mayutilize sufficiently different directions to simultaneously transmitdata belonging to multiple user terminals. A TDMA system may allowmultiple user terminals to share the same frequency channel by dividingthe transmission signal into different time slots, each time slot beingassigned to different user terminal. A TDMA system may implement GSM orsome other standards known in the art. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An OFDM system may implement IEEE 802.11 or some otherstandards known in the art. An SC-FDMA system may utilize interleavedFDMA (IFDMA) to transmit on sub-carriers that are distributed across thesystem bandwidth, localized FDMA (LFDMA) to transmit on a block ofadjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multipleblocks of adjacent sub-carriers. In general, modulation symbols are sentin the frequency domain with OFDM and in the time domain with SC-FDMA. ASC-FDMA system may implement 3GPP-LTE (3rd Generation PartnershipProject Long Term Evolution) or other standards.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a wireless node implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known as aNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology.

A station “STA” may also comprise, be implemented as, or known as a userterminal, an access terminal (“AT”), a subscriber station, a subscriberunit, a mobile station, a remote station, a remote terminal, a useragent, a user device, user equipment, or some other terminology. In someimplementations an access terminal may comprise a cellular telephone, acordless telephone, a Session Initiation Protocol (“SIP”) phone, awireless local loop (“WLL”) station, a personal digital assistant(“PDA”), a handheld device having wireless connection capability, orsome other suitable processing device connected to a wireless modem.Accordingly, one or more aspects taught herein may be incorporated intoa phone (e.g., a cellular phone or smartphone), a computer (e.g., alaptop), a portable communication device, a headset, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music or video device, or a satellite radio), a gamingdevice or system, a global positioning system device, or any othersuitable device that is configured to communicate via a wireless medium.

FIG. 1 is a diagram that illustrates a multiple-access multiple-inputmultiple-output (MIMO) system 100 with access points and user terminals.For simplicity, only one access point 110 is shown in FIG. 1. An accesspoint is generally a fixed station that communicates with the userterminals and may also be referred to as a base station or using someother terminology. A user terminal or STA may be fixed or mobile and mayalso be referred to as a mobile station or a wireless device, or usingsome other terminology. The access point 110 may communicate with one ormore user terminals 120 at any given moment on the downlink and uplink.The downlink (i.e., forward link) is the communication link from theaccess point to the user terminals, and the uplink (i.e., reverse link)is the communication link from the user terminals to the access point. Auser terminal may also communicate peer-to-peer with another userterminal. A system controller 130 couples to and provides coordinationand control for the access points.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects,the AP 110 may be configured to communicate with both SDMA and non-SDMAuser terminals. This approach may conveniently allow older versions ofuser terminals (“legacy” stations) that do not support SDMA to remaindeployed in an enterprise, extending their useful lifetime, whileallowing newer SDMA user terminals to be introduced as deemedappropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≦K≦1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsub-bands with OFDM, and so on. Each selected user terminal may transmituser-specific data to and/or receive user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same number of antennas, or one or more user terminals may havea different number of antennas.

The SDMA system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. The MIMO system 100may also utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, where each time slotmay be assigned to a different user terminal 120.

FIG. 2 illustrates a block diagram of the access point 110 and two userterminals 120 m and 120 x in MIMO system 100. The access point 110 isequipped with N_(t) antennas 224 a through 224 ap. The user terminal 120m is equipped with N_(ut,m) antennas 252 _(ma) through 252 _(mu), andthe user terminal 119 x is equipped with N_(ut,x) antennas 252 _(xa)through 252 _(xu). The access point 110 is a transmitting entity for thedownlink and a receiving entity for the uplink. The user terminal 120 isa transmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via a wirelesschannel, and a “receiving entity” is an independently operated apparatusor device capable of receiving data via a wireless channel. In thefollowing description, the subscript “dn” denotes the downlink, thesubscript “up” denotes the uplink, N_(up) user terminals are selectedfor simultaneous transmission on the uplink, and N_(dn) user terminalsare selected for simultaneous transmission on the downlink. N_(up) mayor may not be equal to N_(dn), and N_(up) and N_(dn) may be staticvalues or may change for each scheduling interval. Beam-steering or someother spatial processing technique may be used at the access point 110and/or the user terminal 120.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. The TX data processor288 processes (e.g., encodes, interleaves, and modulates) the trafficdata for the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252, forexample to transmit to the access point 110.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals may perform spatial processingon its respective data symbol stream and transmit its respective set oftransmit symbol streams on the uplink to the access point 110.

At the access point 110, N_(up) antennas 224 a through 224 _(ap) receivethe uplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(up) received symbol streams from N_(up)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing may be performed in accordancewith the channel correlation matrix inversion (CCMI), minimum meansquare error (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at the access point 110, a TX data processor 210receives traffic data from a data source 208 for N_(dn) user terminalsscheduled for downlink transmission, control data from a controller 230,and possibly other data from a scheduler 234. The various types of datamay be sent on different transport channels. TX data processor 210processes (e.g., encodes, interleaves, and modulates) the traffic datafor each user terminal based on the rate selected for that userterminal. The TX data processor 210 provides N_(dn) downlink data symbolstreams for the N_(dn) user terminals. A TX spatial processor 220performs spatial processing (such as a precoding or beamforming) on theN_(dn) downlink data symbol streams, and provides N_(up) transmit symbolstreams for the N_(up) antennas. Each transmitter unit 222 receives andprocesses a respective transmit symbol stream to generate a downlinksignal. N_(up) transmitter units 222 may provide N_(up) downlink signalsfor transmission from N_(up) antennas 224, for example to transmit tothe user terminals 120.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(up)downlink signals from the access point 110. Each receiver unit 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol streamfor the user terminal 120. The receiver spatial processing may beperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal. Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(up,eff). The controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point 110. The controllers 230and 280 may also control the operation of various processing units atthe access point 110 and user terminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the wireless communication system100. The wireless device 302 is an example of a device that may beconfigured to implement the various methods described herein. Thewireless device 302 may implement an access point 110 or a user terminal120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 may perform logical and arithmetic operations based onprogram instructions stored within the memory 306. The instructions inthe memory 306 may be executable to implement the methods describedherein.

The processor 304 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transceiver antennas 316 may be attached tothe housing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Certain aspects of the present disclosure support transmitting an uplink(UL) signal from multiple STAs to an AP. In some embodiments, the ULsignal may be transmitted in a multi-user MIMO (MU-MIMO) system.Alternatively, the UL signal may be transmitted in a multi-user FDMA(MU-FDMA) or similar FDMA system. Specifically, FIGS. 4-7 illustrateUL-MU-MIMO transmissions 410A, 410B, that would apply equally to UL-FDMAtransmissions. In these embodiments, UL-MU-MIMO or UL-FDMA transmissionscan be sent simultaneously from multiple STAs to an AP and may createefficiencies in wireless communication.

FIG. 4 is a time sequence diagram illustrating an example of anUL-MU-MIMO protocol 400 that may be used for UL communications. As shownin FIG. 4 and in conjunction with FIG. 1, an AP 110 may transmit a clearto transmit (CTX) message 402 to the user terminals 120 indicating whichSTAs may participate in the UL-MU-MIMO scheme, such that a particularSTA knows to start an UL-MU-MIMO. An example of a CTX frame structure isdescribed more fully below with reference to FIG. 10.

Once a user terminal 120 receives a CTX message 402 from the AP 110where the user terminal is listed, the user terminal may transmit theUL-MU-MIMO transmission 410. In FIG. 4, STA 120A and STA 120B transmitUL-MU-MIMO transmission 410A and 410B containing physical layerconvergence protocol (PLCP) protocol data units (PPDUs). Upon receivingthe UL-MU-MIMO transmission 410, the AP 110 may transmit blockacknowledgments (BAs) 470 to the user terminals 120.

Not all APs or user terminals 120 may support UL-MU-MIMO or UL-FDMAoperation. A capability indication from a user terminal 120 may beindicated in a high efficiency wireless (HEW) capability element that isincluded in an association request or probe request and may include abit indicating capability, the maximum number of spatial streams a userterminal 120 can use in a UL-MU-MIMO transmission, the frequencies auser terminal 120 can use in a UL-FDMA transmission, the minimum andmaximum power and granularity in the power backoff, and the minimum andmaximum time adjustment a user terminal 120 can perform.

A capability indication from an AP may be indicated in a HEW capabilityelement that is included in an association response, beacon or proberesponse and may include a bit indicating capability, the maximum numberof spatial streams a single user terminal 120 can use in a UL-MU-MIMOtransmission, the frequencies a single user terminal 120 can use in aUL-FDMA transmission, the required power control granularity, and therequired minimum and maximum time adjustment a user terminal 120 shouldbe able to perform.

In one embodiment, capable user terminals 120 may request to a capableAP to be part of the UL-MU-MIMO (or UL-FDMA) protocol by sending amanagement frame to AP indicating request for enablement of the use ofUL-MU-MIMO feature. In one aspect, an AP 110 may respond by granting theuse of the UL-MU-MIMO feature or denying it. Once the use of theUL-MU-MIMO is granted, the user terminal 120 may expect a CTX message402 at a variety of times. Additionally, once a user terminal 120 isenabled to operate the UL-MU-MIMO feature, the user terminal 120 may besubject to follow a certain operation mode. If multiple operation modesare possible, an AP may indicate to the user terminal 120 which mode touse in a HEW capability element or in an operation element. In oneaspect the user terminals 120 can change the operation modes andparameters dynamically during operation by sending a different operatingelement to the AP 110. In another aspect the AP 110 may switch operationmodes dynamically during operation by sending an updated operatingelement to a user terminal 120 or in a beacon. In another aspect, theoperation modes may be indicated in the setup phase and may be setup peruser terminal 120 or for a group of user terminals 120. In anotheraspect the operation mode may be specified per traffic identifier (TID).

FIG. 5 is a time sequence diagram that, in conjunction with FIG. 1,illustrates an example of an operation mode of a UL-MU-MIMOtransmission. In this embodiment, a user terminal 120 receives a CTXmessage 402 from an AP 110 and sends an immediate response to the AP110. The response may be in the form of a clear to send (CTS) 408 oranother similar signal. In one aspect, requirement to send a CTS may beindicated in the CTX message 402 or may be indicated in the setup phaseof the communication. As shown in FIG. 5, STA 120 A and STA 120B maytransmit a CTS 1 408A and CTS 2 408B message in response to receivingthe CTX message 402. The modulation and coding scheme (MCS) of the CTS 1408A and CTS 2 408B may be based on the MCS of the CTX message 402. Inthis embodiment, CTS 1 408A and CTS 2 408B contain the same bits and thesame scrambling sequence so that they may be transmitted to the AP 110at the same time. The duration field of the CTS 408 signals may be basedon the duration field in the CTX by removing the time for the CTX PPDU.The UL-MU-MIMO transmission 410A and 410B are then sent by the STAs 120Aand 120B as listed in the CTX 402 signals. The AP 110 may then sendacknowledgment (ACK) signals the STAs 120A and 120B. In some aspects,the ACK signals may be serial ACK signals to each station or BAs. Insome aspects the ACKs may be polled. This embodiment createsefficiencies by simultaneously transmitting CTS 408 signals frommultiple STAs to an AP 110 instead of sequentially, which saves time andreduces the possibility of interference.

FIG. 6 is a time sequence diagram that, in conjunction with FIG. 1,illustrates another example of an operation mode of a UL-MU-MIMOtransmission. In this embodiment, user terminals 120A and 120B receive aCTX message 402 from an AP 110 and are allowed to start and UL-MU-MIMOtransmission a time (T) 406 after the end of the PPDU carrying the CTXmessage 402. The T 406 may be a short interframe space (SIFS), pointinterframe space (PIFS), or another time potentially adjusted withadditional offsets as indicated by an AP 110 in the CTX message 402 orvia a management frame. The SIFS and PIFS time may be fixed in astandard or indicated by an AP 110 in the CTX message 402 or in amanagement frame. The benefit of T 406 may be to improve synchronizationor to allow user terminals 120A and 120B time to process the CTX message402 or other messages before transmission.

Referring to FIGS. 4-6, in conjunction with FIG. 1, the UL-MU-MIMOtransmission 410 may have the same duration. The duration of theUL-MU-MIMO transmission 410 for user terminals utilizing the UL-MU-MIMOfeature may be indicated in the CTX message 402 or during the setupphase. To generate a PPDU of the required duration, a user terminal 120may build a PLCP service data unit (PSDU) so that the length of the PPDUmatches the length indicated in the CTX message 402. In another aspect,a user terminal 120 may adjust the level of data aggregation in a mediaaccess control (MAC) protocol data unit (A-MPDU) or the level of dataaggregation in a MAC service data units (A-MSDU) to approach the targetlength. In another aspect, a user terminal 120 may add end of file (EOF)padding delimiters to reach the target length. In another approach thepadding or the EOF pad fields are added at the beginning of the A-MPDU.One of the benefits of having all the UL-MU-MIMO transmissions the samelength is that the power level of the transmission will remain constant.

In some embodiments, a user terminal 120 may have data to upload to theAP but the user terminal 120 has not received a CTX message 402 or othersignal indicating that the user terminal 120 may start a UL-MU-MIMOtransmission.

In one operation mode, the user terminals 120 may not transmit outsidean UL-MU-MIMO transmission opportunity (TXOP) (e.g., after CTX message402). In another operation mode, user terminals 120 may transmit framesto initialize a UL-MU-MIMO transmission, and then may transmit duringthe UL-MU-MIMO TXOP, if for example, they are instructed to do so in aCTX message 402. In one embodiment, the frame to initialize a UL-MU-MIMOtransmission may be a request to transmit (RTX), a frame specificallydesigned for this purpose (an example of a RTX frame structure isdescribed more fully below with reference to FIG. 9). The RTX frames maybe the only frames a user terminal 120 is allowed to use to initiate aUL MU MIMO TXOP. In one embodiment, the user terminal may not transmitoutside an UL-MU-MIMO TXOP other than by sending an RTX. In anotherembodiment, a frame to initialize an UL MU MIMO transmission may be anyframe which indicates to an AP 110 that a user terminal 120 has data tosend. It may be pre-negotiated that these frames indicate a UL MU MIMOTXOP request. For example, the following may be used to indicate that auser terminal 120 has data to send and is requesting an UL MU MIMO TXOP:an RTS, a data frame or QoS Null frame with bits 8-15 of the QoS controlframe set to indicate more data, or a PS poll. In one embodiment, theuser terminal may not transmit outside an UL MU MIMO TXOP other than bysending frames to trigger this TXOP, where this frame may be an RTS, PSpoll, or QOS null. In another embodiment, the user terminal may sendsingle user uplink data as usual, and may indicate a request for a UL MUMIMO TXOP by setting bits in the QoS control frame of its data packet.FIG. 7 is a time sequence diagram illustrating, in conjunction with FIG.1, an example where the frame to initialize a UL-MU-MIMO is a RTX 701.In this embodiment the user terminal 120 sends to the AP 110 a RTX 701that includes information regarding the UL-MU-MIMO transmission. Asshown in FIG. 7, the AP 110 may respond to the RTX 701 with a CTXmessage 402 granting an UL-MU-MIMO TXOP to send the UL-MU-MIMOtransmission 410 immediately following the CTX message 402. In anotheraspect, the AP 110 may respond with a CTS that grants a single-user (SU)UL TXOP. In another aspect, the AP 110 may respond with a frame (e.g.,ACK or CTX with a special indication) that acknowledges the reception ofthe RTX 701 but does not grant an immediate UL-MU-MIMO TXOP. In anotheraspect, the AP 110 may respond with a frame that acknowledges thereception of the RTX 701, does not grant an immediate UL-MU-MIMO TXOP,but grants a delayed UL-MU-MIMO TXOP and may identify the time of theTXOP is granted. In this embodiment, the AP 110 may send a CTX message402 to start the UL-MU-MIMO at the granted time.

In another aspect, the AP 110 may respond to the RTX 701 with an ACK orother response signal which does not grant the user terminal 120 anUL-MU-MIMO transmission but indicates that the user terminal 120 shallwait for a time (T) before attempting another transmission (e.g.,sending another RTX). In this aspect the time (T) may be indicated bythe AP 110 in the setup phase or in the response signal. In anotheraspect an AP 110 and a user terminal 120 may agree on a time which theuser terminal 120 may transmit a RTX 701, RTS, PS-poll, or any otherrequest for a UL-MU-MIMO TXOP.

In another operation mode, user terminals 120 may transmit requests forUL-MU-MIMO transmissions 410 in accordance with regular contentionprotocol. In another aspect, the contention parameters for userterminals 120 using UL-MU-MIMO are set to a different value than forother user terminals that are not using the UL-MU-MIMO feature. In thisembodiment, the AP 110 may indicate the value of the contentionparameters in a beacon, association response or through a managementframe. In another aspect, the AP 110 may provide a delay timer thatprevents a user terminal 120 from transmitting for a certain amount oftime after each successful UL-MU-MIMO TXOP or after each RTX, RTS,PS-poll, or QoS null frame. The timer may be restarted after eachsuccessful UL-MU-MIMO TXOP. In one aspect, the AP 110 may indicate thedelay timer to user terminals 120 in the setup phase or the delay timermay be different for each user terminal 120. In another aspect, the AP110 may indicate the delay timer in the CTX message 402 or the delaytimer may be dependent on the order of the user terminals 120 in the CTXmessage 402, and may be different for each terminal.

In another operational mode, the AP 110 may indicate a time intervalduring which the user terminals 120 are allowed to transmit a UL-MU-MIMOtransmission. In one aspect, the AP 110 indicates a time interval to theuser terminals 120 during which the user terminals are allowed to send aRTX or RTS or other request to the AP 110 to ask for an UL-MU-MIMOtransmission. In this aspect, the user terminals 120 may use regularcontention protocol. In another aspect, the user terminals may notinitiate a UL-MU-MIMO transmission during the time interval but the AP110 may send a CTX or other message to the user terminals to initiatethe UL-MU-MIMO transmission.

In certain embodiments, a user terminal 120 enabled for UL-MU-MIMO mayindicate to an AP 110 that it requests an UL-MU-MIMO TXOP because it hasdata pending for UL. In one aspect, the user terminal 120 may send a RTSor a PS-poll to request a UL-MU-MIMO TXOP. In another embodiment, theuser terminal 120 may send any data frame, including a quality ofservice (QoS) null data frame, where the bits 8-15 of the QoS controlfield indicate a non-empty queue. In this embodiment the user terminal120 may determine during the setup phase which data frames (e.g., RTS,PS-poll, QoS null, etc.) will trigger a UL-MU-MIMO transmission when thebits 8-15 of the QoS control field indicate a non-empty queue. In oneembodiment, the RTS, PS-poll, or QoS null frames may include a 1 bitindication allowing or disallowing the AP 110 to respond with a CTXmessage 402. In another embodiment, the QoS null frame may include TXpower information and a per TID queue information. The TX powerinformation and per TID queue information may be inserted in the twobytes of the sequence control and QoS controls fields in a QoS nullframe and the modified QoS null frame may be sent to the AP 110 torequest a UL-MU-MIMO TXOP. In another embodiment, referring to FIGS. 1and 7, the user terminal 120 may send a RTX 701 to request a UL-MU-MIMOTXOP.

In response to receiving an RTS, RTX, PS-poll or QoS null frame, orother trigger frame as described above, an AP 110 may send a CTX message402. In one embodiment, referring to FIG. 7, after the transmission ofthe CTX message 402 and the completion of the UL-MU-MIMO transmissions410A and 410B, TXOP returns to the STAs 120A and 120B which can decideon how to use the remaining TXOP. In another embodiment, referring toFIG. 7, after the transmission of the CTX message 402 and the completionof the UL-MU-MIMO transmissions 410A and 410B, TXOP remains with the AP110 and the AP 110 may use the remaining TXOP for additional UL-MU-MIMOtransmissions by sending another CTX message 402 to either STAs 120A and120B or to other STAs.

FIG. 8 is a message timing diagram of one embodiment of multi-useruplink communication. Message exchange 800 shows communication ofwireless messages between an AP 110 and three stations 120 a-c. Messageexchange 800 indicates that each of STAs 120 a-c transmits arequest-to-transmit (RTX) message 802 a-c to the AP 110. Each of RTXmessages 802 a-c indicate that the transmitting station 120 a-c has dataavailable to be transmitted to the AP 110.

After receiving each of RTX messages 802 a-c, the AP 110 may respondwith a message indicating that the AP 110 has received the RTX. As shownin FIG. 8, the AP 110 transmits ACK messages 803 a-c in response to eachRTX messages 802 a-c. In some embodiments, the AP 110 may transmit amessage (e.g., a CTX message) indicating that each of the RTX messages802 a-c has been received but that the AP 110 has not granted atransmission opportunity for the stations 120 a-c to uplink data. InFIG. 8, after sending ACK message 803 c, the AP 110 transmits a CTXmessage 804. In some aspects, the CTX message 804 is transmitted to atleast the stations STA 120 a-c. In some aspects, the CTX message 804 isbroadcast. In some aspects, the CTX message 804 indicates which stationsare granted permission to transmit data to the AP 110 during atransmission opportunity. The starting time of the transmissionopportunity and its duration may be indicated in the CTX message 804 insome aspects. For example, the CTX message 804 may indicate that thestations STA 120 a-c should set their network allocation vectors to beconsistent with NAV 812.

At a time indicated by the CTX message 804, the three stations 120 a-ctransmit data 806 a-c to the AP 110. The data 806 a-c are transmitted atleast partially concurrently during the transmission opportunity. Thetransmissions of data 806 a-c may utilize uplink multi-user multipleinput, multiple output transmissions (UL-MU-MIMO) or uplink frequencydivision multiple access (UL-FDMA).

FIG. 9 is a diagram of one embodiment of a RTX frame 900. The RTX frame900 includes a frame control (FC) field 910, a duration field 915(optional), a transmitter address (TA)/allocation identifier (AID) field920, a receiver address (RA)/basic service set identifier (BSSID) field925, a TID field 930, an estimated transmission (TX) time field 950, anda TX power field 970. The FC field 910 indicates a control subtype or anextension subtype. The duration field 815 indicates to any receiver ofthe RTX frame 900 to set the network allocation vector (NAV). In oneaspect, the RTX frame 900 may not have a duration field 815. The TA/AIDfield 920 indicates the source address which can be an AID or a full MACaddress. The RA/BSSID field 925 indicates the RA or BSSID. In one aspectthe RTX frame may not contain a RA/BSSID field 925. The TID field 930indicates the access category (AC) for which the user has data. TheEstimated TX time field 950 indicates the time requested for the UL-TXOPand may be the time required for a user terminal 120 to send all thedata in its buffer at the current planned MCS. The TX power field 970indicates the power at which the frame is being transmitted and can beused by the AP to estimate the link quality and adapt the power backoffindication in a CTX frame.

As discussed above, the CTX message 402 may be used in a variety ofcommunications. FIG. 10 is a diagram of an example of a CTX frame 1000structure. In this embodiment, the CTX frame 1000 is a control framethat includes a frame control (FC) field 1005, a duration field 1010, areceiver address field 1014, a transmitter address (TA) field 1015, acontrol (CTRL) field 1020, a PPDU duration field 1025, a STA info field1030, and a frame check sequence (FCS) field 1080. The FC field 1205indicates a control subtype or an extension subtype. The duration field1010 indicates to any receiver of the CTX frame 1000 to set the networkallocation vector (NAV). In some embodiments the RA 1014 fieldidentifies a group of STAs through a multicast MAC address. The TA field1015 indicates the transmitter address or a BSSID. The CTRL field 1020is a generic field that may include information regarding the format ofthe remaining portion of the frame (e.g., the number of STA info fieldsand the presence or absence of any subfields within a STA info field),indications for rate adaptation for the user terminals 120, indicationof allowed TID, and indication that a CTS must be sent immediatelyfollowing the CTX frame 1000. The CTRL field 1020 may also indicate ifthe CTX frame 1000 is being used for UL MU MIMO or for UL FDMA or both,indicating whether a Nss or Tone allocation field is present in the STAInfo field 1030.

Alternatively, the indication of whether the CTX is for UL MU MIMO orfor UL FDMA can be based on the value of the subtype. Note that UL MUMIMO and UL FDMA operations can be jointly performed by specifying to aSTA both the spatial streams to be used and the channel to be used, inwhich case both fields are present in the CTX; in this case, the Nssindication is referred to a specific tone allocation. The PPDU duration1025 field indicates the duration of the following UL-MU-MIMO PPDU thatthe user terminals 120 are allowed to send. The STA Info 1030 fieldcontains information regarding a particular STA and may include aper-STA (per user terminal 120) set of information (see STA Info 1 1030and STA Info N 1075). The STA Info 1030 field may include an AID or MACaddress field 1032 which identifies a STA, a number of spatial streamsfield (Nss) 1034 field which indicates the number of spatial streams aSTA may use (in an UL-MU-MIMO system), a Time Adjustment 1036 fieldwhich indicates a time that a STA should adjust its transmissioncompared to the reception of a trigger frame (the CTX in this case), aPower Adjustment 1038 field which indicates a power backoff a STA shouldtake from a declared transmit power, a Tone Allocation 1040 field whichindicates the tones or frequencies a STA may use (in a UL-FDMA system),an Allowed TID 1042 field which indicates the allowable TID, an AllowedTX Mode 1044 field which indicates the allowed TX modes, and a MCS 1046field which indicates the MCS the STA should use. A user terminal 120receiving a CTX with a Allowed TID 1042 indication may be allowed totransmit data only of that TID, data of the same or higher TID, data ofthe same or lower TID, any data, or only data of that TID first, then ifno data is available, data of other TIDs. The FCS 1080 field indicatesthe carries an FCS value used for error detection of the CTX frame 1000.

FIG. 11 shows a variety of message exchanges that demonstrateacknowledgment methods that may be employed by one or more of thedisclosed embodiments. Message exchange 1104 a shows a multi-user uplink1105 a from at least two different stations 120 a and 120 b, beingtransmitted to an access point 110. In message exchange 1104 a, only onestation is allowed to set the block acknowledgment policy to immediateblock ack or normal acknowledgment (acknowledgment of a single frame).In message exchange 1104, STA 120 a has an immediate blockacknowledgement policy. Therefore, after reception of the multi-useruplink PPDU 1105 a, a block acknowledgment is transmitted to STA 120 a.After a period of time, STA 120 b transmits a block acknowledgmentrequest 1115 a to the AP 110. Upon receiving the block acknowledgmentrequest 1115 a, the AP 110 transmits the block acknowledgment 1120 a tothe STA 120 b.

Message exchange 1104 b shows a multi-user uplink PPDU 1105 dtransmitted by at least three different stations 120 a, 120 b, and 120c. In response to receiving the multi-user uplink 1105 b, the AP 110transmits a first block ack 1110 b to STA 120 a and a second block ack1115 b to STA 120 b. A third block acknowledgment 1125 b is transmittedto STA 120 c. Two acknowledgment frames 1120 b and 1130 b are alsotransmitted.

Message exchange 1104 c shows a multi-user uplink PPDU 1105 ctransmitted by at least three different stations 120 a, 120 b, and 120c. The uplink 1105 c is received by an access point 110. In theembodiment of 1104 c, the access point may send block acknowledgmentsfor the PPDU's transmitted as part of the uplink transmission 1105 b atany time, with contention. Therefore, after completion of thetransmission of the uplink PPDU 1105 c, the AP 110 transmits separateindividual block acknowledgments 1110 c, 1115 c, and 1120 c to each ofthe stations 120 a-c.

Message exchange 1104 d shows a multi-user uplink PPDU 1105 dtransmitted by at least two stations 120 a and 120 b. After reception ofthe uplink 1105 d, the AP 110 transmits via downlink frequency divisionmultiplexing (FDMA) multiple block acknowledgments 1110 d to the atleast two stations 120 a and 120 b, at least partially concurrently. Insome other aspects, the multiple block acknowledgments 1110 d may betransmitted via downlink multi-user MIMO.

Message exchange 1104 e shows a multi-user uplink PPDU 1105 etransmitted by at least two stations 120 a and 120 b. After reception ofthe uplink 1105 e, the AP 110 transmits a single block acknowledgmentmessage 1110 e to at least two stations 120 a and 120 b.

FIG. 12 is a message flow diagram illustrating a uplink multi usertransmission. The exemplary message exchange 1200 is performed by fourstations STA 120 a-d and an access point 110. Initially, each of thestations 120 a-d transmits an acknowledgment policy message 1202 a-d tothe AP 110. In some aspects, the acknowledgment policy is a request totransmit message. The acknowledgment policy message may indicate howdata transmitted by each of the stations 120 a-d respectively should beacknowledged by the access point. For example, in some aspects, eachacknowledgment policy message 1202 a-d may indicate whether the stationrequests an acknowledgment for each message, an immediate blockacknowledgment, or delayed block acknowledgments.

In some aspects, the AP 110 may respond to the acknowledgment policymessages 1202 a-d with a clear to transmit message 1204. In someaspects, one clear to transmit message 1204 will be transmitted to allfour of the stations 120 a-d. In some other aspects, multiple clear totransmit messages may be transmitted (not shown). The clear to transmitmessage may provide information regarding a start time and a duration ofa transmission opportunity during which the stations 120 a-d are grantedpermission to transmit data. In some aspects, the clear to transmitmessage 1204 may indicate to one or more stations a time at which it canexpect an acknowledgement for data sent during the transmissionopportunity. For example, a station may request regular acknowledgmentsin an acknowledgment policy message, such as messages 120 a-d. However,due to the fact that multiple STAs need to be acknowledged after amulti-user transmission, in some aspects not all stations can beacknowledged immediately.

Note that while FIG. 12 shows the clear to transmit message 1204 beingtransmitted immediate after transmission of the acknowledgment policymessages 1202 a-d, in some aspects, a variable amount of time and/orwireless frames may be present between any of the acknowledgment policymessages 1202 a-d and the clear to transmit message 1204.

Therefore, the clear to transmit message 1204 may allow the AP 110 tocoordinate acknowledgment timing for each of the stations expected totransmit during the transmission opportunity. In embodiments thattransmit multiple CTX messages, the acknowledgment timing informationmay be provided in each CTX message, as appropriate for the device towhich each of the multiple CTX messages is transmitted.

In response to receiving the clear to transmit message 1204, each of thestations 120 a-d transmits a data message 1206 a-d respectively to theaccess point 110. The data messages 1206 a-d are transmitted at leastpartially simultaneously. In some aspects, the data messages 1206 a-dmay be transmitted using uplink multi-user MIMO and in some otheraspects the data messages 1206 a-d may be transmitted using uplink FDMA.

After receiving the uplink transmission comprised of data messages1206-d, the AP determines how it should acknowledge each of the datamessages 1206 a-d. In the illustrated aspect, the AP initially respondsto the data messages 1206 a-d by transmitting acknowledgements 1208 a-cto STAs 120, STA 120 b, and STA 120 d. The AP acknowledges STA 120 a,STA 120 b, and STA 120 d immediately after reception of the datamessages 1206 a-d in this aspect because acknowledgment policy messages1202 a-b and 1202 d indicated the stations 120 a-b and 120 d requestedregular acknowledgments and immediate block acknowledgmentsrespectively. The three acknowledgment messages 1208 a-c are transmittedat least partially simultaneously. In some aspects, the acknowledgmentmessages 1208 a-c may be transmitted using downlink multi-user MIMO ordownlink FDMA.

Acknowledgment policy message 1202 c indicated to the AP 110 that STA120 c requests delayed block acknowledgments. Thus, STA 120 c transmitsa block acknowledgment request 1212 c to the AP 110. In response, the AP110 transmits block acknowledgment message 1214.

FIG. 13 is a method of acknowledging a wireless message. The method 1300may be performed, in some aspects, by the wireless device 302, and/or anAP 110 and/or any of STA's 120 discussed above. Process 1300 may providefor the transmission of a plurality of acknowledgment messages to amulti-user transmission at least partially in parallel or concurrently.By transmitting acknowledgment messages concurrently, greaterutilization of a wireless medium may be achieved. For example, in someaspects, process 1300 provides for the transmission of multipleacknowledgments to multiple stations using downlink FDMA or downlinkmulti-user MIMO. In some aspects, this capability allows acknowledgmentsto occur synchronously with their respective data. Thus, a greaterpercentage of the wireless medium utilization can be used for thetransmission of data messages. This contrasts with solution that mightinstead follow a multi-user uplink transmission with a period of serialacknowledgments for each of the multi-user uplink transmissions.

In block 1305, a first wireless message is received from a first stationat least partially concurrently with reception of a second wirelessmessage from a second station. In some aspects, the first and secondwireless messages are received via uplink multi-user MIMO, while inother aspects, the first and second wireless messages are received viauplink frequency division multiple access. (UL-FDMA). In some aspects, athird and possibly fourth wireless message from a third and fourthstation may also be received at least partially concurrently with thefirst and second wireless messages. These third and fourth messages mayalso be part of the UL-FDMA or UL-MU-MIMO transmission.

Some aspects of method 1300 include receiving a message from a stationindicating an acknowledgment policy for the station. For example, theacknowledgment policy message may indicate whether the station requestsregular acknowledgments, immediate block acknowledgments, or delayedblock acknowledgments. In some aspects, an acknowledgment policy messagemay be received from one or more of the first, second, third or fourthstations discussed above.

Some aspects of block 1305 include transmitting one or more clear totransmit message(s) to one or more of the first, second, third, andfourth stations discussed above. In some aspects, the clear to transmitmessages are generated to indicate a time when the first, second, third,and/or fourth messages may be transmitted to the device performingmethod 1300.

In block 1310 a first acknowledgment message is generated in response toreceiving the first wireless message. The first acknowledgment messageis generated to provide an acknowledgment of the first wireless messagereceived in block 1305. The first acknowledgment message may begenerated to acknowledge just the first wireless message, or may begenerated as a block acknowledgment to acknowledge a single frame ormultiple frames. In some aspects, how the first acknowledgment messageis generated is based on an acknowledgment policy for the first station.

In block 1315, a second acknowledgment message is generated in responseto receiving the second wireless message. The second acknowledgementmessage is generated to provide an acknowledgement of the secondwireless message received in block 1305. The second acknowledgmentmessage may be generated to acknowledge just the second wirelessmessage, or may be generated as a block acknowledgment to acknowledge asingle frame or multiple frames. In some aspects, how the secondacknowledgment message is generated is based on an acknowledgment policyfor the second station.

In some aspects, generation of the first and/or second acknowledgmentmessages are based on acknowledgment policy messages received from therespective first and second stations as discussed above. For example,the acknowledgment policy messages may have been decoded to determinethat the first and second stations request immediate blockacknowledgments or acknowledgments of a single frame. Theseacknowledgment policies may allow the device performing process 1300 totransmit acknowledgments to the first and second wireless messages inparallel using downlink multi-user MIMO or downlink FDMA as discussedbelow.

In block 1320, the first and second acknowledgment messages aretransmitted to the first and second stations respectively. The twomessages are transmitted at least partially concurrently. In someaspects, the concurrent transmission is accomplished using downlinkfrequency division multiple access (DL-FDMA) and in some other aspects,the transmission is accomplished using downlink multi-user MIMO(DL-MU-MIMO).

In some aspects, the first acknowledgment message is transmitted on aspatial stream that is based on a second spatial stream upon which thefirst wireless message was received. For example, in some aspects, thefirst acknowledgment message is transmitted over the same spatial streamupon which the first wireless message was received. Similarly,transmission of the second acknowledgment message may be performed overa spatial stream that is based upon a spatial stream upon which thesecond wireless message was received. Similar to the example above forthe first wireless message, in some aspects, the second wireless messagemay also be transmitted over the same spatial stream over which thesecond wireless message was received.

In some aspects that use DL-FMDA to transmit the acknowledgmentmessages, the first acknowledgment message may be transmitted over afrequency band over which the first wireless message was received, orthe frequency band may at least be based on the frequency band overwhich the first wireless message was received. Similarly, in someaspects, the second acknowledgment message may be transmitted over thesame frequency band over which the second wireless message was received,or at least a frequency band that is based on the frequency band of thesecond wireless message.

In some aspects, acknowledgment policy messages that may be receivedfrom the third and potentially fourth station discussed above mayindicate that these stations request delayed block acknowledgments. Inthese aspects, acknowledgments for the third and possibly fourthwireless messages may not be generated in immediate response toreception of the third and fourth wireless messages in block 1305, butmay instead be transmitted at a later time.

For example, in some aspects, the acknowledgments to the third andpotentially fourth wireless messages discussed above may be transmittedto the third and fourth devices in response to reception of a blockacknowledgment request from each of the third and fourth stationsrespectively, as shown for example, in FIG. 12 with respect to blockacknowledgment request 1212 c and block acknowledgment 1214.

FIG. 14 is a flowchart of a method of receiving acknowledgment of awireless message. The method 1400 may be performed, in some aspects, bythe wireless device 302, and/or an AP 110 and/or any of STA's 120discussed above.

Process 1400 may provide for the reception of a plurality ofacknowledgment messages for a multi-user transmission at least partiallyin parallel or concurrently. By multiple devices receivingacknowledgment messages concurrently, greater utilization of a wirelessmedium may be achieved. For example, in some aspects, process 1400provides for the reception of multiple acknowledgments by multiplestations using downlink FDMA or downlink multi-user MIMO. In someaspects, this capability allows acknowledgments to occur synchronouslywith their respective data. Thus, a greater percentage of the wirelessmedium utilization can be used for the transmission of data messages.This contrasts with solution that might instead follow a multi-useruplink transmission with a period of serial acknowledgments for each ofthe multi-user uplink transmissions.

In block 1405, a first wireless device transmits a first wirelessmessage to a second wireless device at least partially concurrently witha transmission by a third wireless device of a second wireless messageto the second wireless device. In some aspects, the transmission of thefirst wireless message is part of a multi-user uplink transmission by aplurality of stations to an access point. In some aspects, thetransmission is performed using uplink multi-user MIMO, while in someother aspects, the transmission is performed using uplink FDMA. Forexample, the first wireless message may be transmitted over a firstspatial stream while the second wireless message is transmitted by thethird wireless device over a second spatial stream. Alternatively, thefirst wireless message may be transmitted over a first frequency whilethe second wireless message is transmitted over a second frequency.

In some aspects, of process 1400, a third wireless message is generated.The third wireless message indicates an acknowledgment policy foracknowledging the first wireless message. For example, in some aspects,the third wireless message is a request to transmit message. The thirdmessage may be transmitted to the second wireless device, which may bean access point in some aspects. In some aspects, the third wirelessmessage is generated to indicate an acknowledgment policy of immediateblock acknowledgment or normal acknowledgment (acknowledgment of asingle frame).

Some aspects of process 1400 include receiving a clear to transmitmessage, and decoding the clear to transmit message to determine a timeto transmit the first wireless message. These aspects may also includetransmitting the first wireless message in block 1405 at the determinedtime.

In block 1410, an acknowledgement message for the first wireless messageis received from the second wireless device. The acknowledgment isreceived at least partially concurrently with at least a portion of asecond acknowledgment message, transmitted by the second wirelessdevice, for the second wireless message. The second acknowledgmentmessage may not be addressed to the first wireless device, but at leasta portion of it, for example, at least a preamble, may be received bythe first wireless device.

In some aspects, the third wireless message discussed above may begenerated to indicate an acknowledgment policy of delayed blockacknowledgment. In these aspects, process 1400 may include transmissionof a fourth wireless message to the second wireless device at leastpartially concurrently with a transmission by a fourth wireless deviceor the third wireless device of a fifth wireless message to the secondwireless device. The fourth and fifth wireless messages may comprise asecond multi-user uplink transmission transmitted using eitherUL-MU-MIMO or UL-FDMA.

After transmission of the fourth wireless message, a blockacknowledgment message may be transmitted by the first wireless deviceto the second wireless device. This block acknowledgment request messagemay request acknowledgment of at least the fourth wireless message.After transmitting the block acknowledgment request, a blockacknowledgment may be received from the second wireless device, in someaspects indicating whether the fourth wireless message was properlyreceived by the second wireless device. Thus, even though the fourthwireless message was transmitted currently with the fifth wirelessmessage by another wireless device, the acknowledgment of the fourthwireless message may be independent of any acknowledgment of the fifthwireless message.

A person/one having ordinary skill in the art would understand thatinformation and signals can be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that can bereferenced throughout the above description can be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

Various modifications to the implementations described in thisdisclosure can be readily apparent to those skilled in the art, and thegeneric principles defined herein can be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the claims, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other implementations.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable sub-combination.Moreover, although features can be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination can be directed to asub-combination or variation of a sub-combination.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium.Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer readable medium may comprisenon-transitory computer readable medium (e.g., tangible media). Inaddition, in some aspects computer readable medium may comprisetransitory computer readable medium (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method of wireless communication, comprising:receiving a first wireless message from a first station at leastpartially concurrently with receiving a second wireless message from asecond station; receiving a third wireless message from a third stationat least partially concurrently with the first wireless message and thesecond wireless message; receiving a fourth wireless message from thethird station, the fourth wireless message indicating an acknowledgmentpolicy for the third station; generating a first acknowledgment messagein response to receiving the first wireless message; generating a secondacknowledgement message in response to receiving the second wirelessmessage; transmitting the first acknowledgment message to the firststation at least partially concurrently with transmitting the secondacknowledgement message to the second station; receiving a fifthwireless message from the third station after receiving the fourthwireless message, the fifth wireless message requesting a blockacknowledgment for the third station; generating a third acknowledgmentmessage in response to receiving the fifth wireless message; generatinga clear to transmit message, the clear to transmit message indicating atime when the third acknowledgment will be transmitted and a seconddifferent time when a fourth acknowledgment will be transmitted to afourth station; transmitting the clear to transmit message to the thirdstation and the fourth station; and transmitting the thirdacknowledgment message to the third station.
 2. The method of claim 1,wherein the first acknowledgment message is generated as a blockacknowledgment and the second acknowledgment message is generated as anacknowledgment of a single frame.
 3. The method of claim 1, wherein thefirst acknowledgment message is generated as a block acknowledgment andthe second acknowledgment message is generated as a blockacknowledgment.
 4. The method of claim 1, further comprising: receivinga sixth wireless message from the first station, the sixth wirelessmessage indicating an acknowledgment policy for the first station; andtransmitting the first acknowledgment message based on theacknowledgment policy for the first station.
 5. The method of claim 4,further comprising: determining the first station requests immediateblock acknowledgements based on the sixth wireless message; andtransmitting the first acknowledgment message based on the determining.6. The method of claim 1, wherein the fifth wireless message from thethird station indicates the third station requests delayed blockacknowledgments, and wherein the third acknowledgment message istransmitted to the third station after completion of the transmissionsof the first and second wireless messages based on the fifth wirelessmessage.
 7. The method of claim 1, further comprising: receiving thefirst wireless message over a first spatial stream; receiving the secondwireless message over a second spatial stream; determining a thirdspatial stream based on the first spatial stream; determining a fourthspatial stream based on the second spatial stream; wherein the firstacknowledgment message is transmitted over the third spatial stream; andwherein the second acknowledgment message is transmitted over the fourthspatial stream.
 8. The method of claim 1, further comprising: whereinthe first wireless message is received over a first frequency; whereinthe second wireless message is received over a second frequency;determining a third frequency based on the first frequency; determininga fourth frequency based on the second frequency; wherein the firstacknowledgment message is transmitted over the third frequency; andwherein the second acknowledgment message is transmitted over the fourthfrequency.
 9. An apparatus for wireless communication, comprising: areceiver configured to receive a first wireless message from a firststation at least partially concurrently with receiving a second wirelessmessage from a second station, and wherein the receiver is furtherconfigured to receive a third wireless message from a third station atleast partially concurrently with the first wireless message and thesecond wireless message, and wherein the receiver is further configuredto receive a fourth wireless message from the third station, the fourthwireless message indicating an acknowledgment policy for the thirdstation; a hardware processor configured to generate a firstacknowledgment message in response to receiving the first wirelessmessage, and generate a second acknowledgement message in response toreceiving the second wireless message; and a transmitter configured totransmit the first acknowledgment message to the first station at leastpartially concurrently with transmitting the second acknowledgementmessage to the second station, wherein the receiver is furtherconfigured to receive a fifth wireless message from the third stationafter receiving the fourth wireless message, the fifth wireless messagerequesting a block acknowledgment for the third station, wherein theprocessor is further configured to generate a third acknowledgmentmessage in response to receiving the fifth wireless message, wherein theprocessor is further configured to generate a clear to transmit message,the clear to transmit message indicating a time when the thirdacknowledgment will be transmitted and a second different time when afourth acknowledgment will be transmitted to a fourth station, whereinthe transmitter is further configured to transmit the clear to transmitmessage to the third station and the fourth station, and wherein thetransmitter is further configured to transmit the third acknowledgementmessage to the third station.
 10. The apparatus of claim 9, wherein theprocessor is further configured to generate the first acknowledgmentmessage as a block acknowledgment and the processor is furtherconfigured to generate the second acknowledgment message as a blockacknowledgment.
 11. The apparatus of claim 9, wherein the processor isfurther configured to generate the first acknowledgment message as ablock acknowledgment and the processor is further configured to generatethe second acknowledgment message as an acknowledgment of a singleframe.
 12. The apparatus of claim 9, wherein the receiver is furtherconfigured to receive a sixth wireless message from the first station,the sixth wireless message indicating an acknowledgment policy for thefirst station, and wherein the transmitter is further configured totransmit the first acknowledgment message based on the acknowledgmentpolicy for the first station.
 13. The apparatus of claim 12, wherein theprocessor is further configured to determine the first station requestsimmediate block acknowledgements based on the sixth wireless message,and the transmitter is further configured to transmit the firstacknowledgment message based on the determining.
 14. The apparatus ofclaim 9, wherein the fifth wireless message from the third stationindicates the third station requests delayed block acknowledgments, andwherein the transmitter is further configured to transmit the thirdacknowledgment message to the third station after completion of thetransmissions of the first and second wireless messages based on thefifth wireless message.
 15. The apparatus of claim 9, wherein thereceiver is further configured to receive the first wireless messageover a first spatial stream and receive the second wireless message overa second spatial stream, and wherein the processor is further configuredto determine a third frequency based on the first spatial stream anddetermine a fourth frequency based on the second spatial stream, and thetransmitter is further configured to transmit the first acknowledgmentmessage over the third spatial stream and transmit the secondacknowledgment message over the fourth spatial stream.
 16. The apparatusof claim 9, wherein the receiver is further configured to receive thefirst wireless message over a first frequency and receive the secondwireless message over a second frequency, and wherein the processor isfurther configured to determine a third frequency based on the firstfrequency and determine a fourth frequency based on the secondfrequency, and the transmitter is further configured to transmit thefirst acknowledgment message over the third frequency and transmit thesecond acknowledgment message over the fourth frequency.
 17. Theapparatus of claim 9, wherein the clear to transmit message indicatesthe third station has permission to transmit a sixth wireless message.18. An apparatus for wireless communication, comprising: means forreceiving a first wireless message from a first station at leastpartially concurrently with receiving a second wireless message from asecond station, wherein the means for receiving is further configured toreceive a third wireless message from a third station at least partiallyconcurrently with the first wireless message and the second wirelessmessage, and wherein the means for receiving is further configured toreceive a fourth wireless message from the third station, the fourthwireless message indicating an acknowledgment policy for the thirdstation; means for generating a first acknowledgment message in responseto receiving the first wireless message and a second acknowledgementmessage in response to receiving the second wireless message; and meansfor transmitting the first acknowledgment message to the first stationat least partially concurrently with transmitting the secondacknowledgement message to the second station, wherein the means forreceiving is further configured to receive a fifth wireless message fromthe third station after receiving the fourth wireless message, the fifthwireless message requesting a block acknowledgment for the thirdstation, wherein the means for generating is further configured togenerate a third acknowledgment message in response to receiving thefifth wireless message, wherein the means for generating is furtherconfigured to generate a clear to transmit message, the clear totransmit message generated to indicate a time when the thirdacknowledgment will be transmitted and a second different time when afourth acknowledgment will be transmitted to a fourth station, whereinthe means for transmitting is further configured to transmit the clearto transmit message to the third station and the fourth station, andwherein the means for transmitting is further configured to transmit thethird acknowledgment message to the third station.
 19. The apparatus ofclaim 18, wherein the first acknowledgment message is generated as ablock acknowledgment and the second acknowledgment message is generatedas an acknowledgment of a single frame.
 20. The apparatus of claim 18,wherein the first acknowledgment message is generated as a blockacknowledgment and the second acknowledgment message is generated as ablock acknowledgment.
 21. The apparatus of claim 18, wherein the meansfor receiving is further configured to receive a sixth wireless messagefrom the first station, the sixth wireless message indicating anacknowledgment policy for the first station, and wherein the means fortransmitting is further configured to transmit the first acknowledgmentmessage based on the acknowledgment policy for the first station. 22.The apparatus of claim 21, wherein the means for generating is furtherconfigured to determine the first station requests immediate blockacknowledgements based on the sixth wireless message, and wherein themeans for transmitting is further configured to transmit the firstacknowledgment message based on the determining.
 23. The apparatus ofclaim 18, wherein the fifth wireless message from the third stationindicates the third station requests delayed block acknowledgments, andwherein the means for transmitting is further configured to transmit thethird acknowledgment message to the third station after completion ofthe transmissions of the first and second wireless messages based on thefifth wireless message.
 24. The apparatus of claim 18, wherein the meansfor receiving is further configured to receive the first wirelessmessage over a first spatial stream and receive the second wirelessmessage over a second spatial stream, wherein the means for generatingis further configured to determine a third spatial stream based on thefirst spatial stream and determine a fourth spatial stream based on thesecond spatial stream, and wherein the means for transmitting is furtherconfigured to transmit the first acknowledgment message over the thirdspatial stream and transmit the second acknowledgment message over thefourth spatial stream.
 25. The apparatus of claim 18, wherein the meansfor receiving is further configured to receive the first wirelessmessage over a first frequency and receive the second wireless messageover a second frequency, wherein the means for generating is furtherconfigured to determine a third frequency based on the first frequencyand determine a fourth frequency based on the second frequency, andwherein the means for transmitting is further configured to transmit thefirst acknowledgment message over the third frequency and transmit thesecond acknowledgment message over the fourth frequency.
 26. Theapparatus of claim 18, wherein the clear to transmit clear to transmitmessage indicates the third station has permission to transmit a sixthwireless message.
 27. A non-transitory computer-readable mediumcomprising instructions that when executed by a computer causes thecomputer to perform a method of wireless communication, the methodcomprising: receiving a first wireless message from a first station atleast partially concurrently with receiving a second wireless messagefrom a second station; receiving a third wireless message from a thirdstation at least partially concurrently with the first wireless messageand the second wireless message; receiving a fourth wireless messagefrom the third station, the fourth wireless message indicating anacknowledgment policy for the third station; generating a firstacknowledgment message in response to receiving the first wirelessmessage; generating a second acknowledgement message in response toreceiving the second wireless message; transmitting the firstacknowledgment message to the first station at least partiallyconcurrently with transmitting the second acknowledgement message to thesecond station; receiving a fifth wireless message from the thirdstation after receiving the fourth wireless message, the fifth wirelessmessage requesting a block acknowledgment for the third station;generating a third acknowledgment message in response to receiving thefifth wireless message; generating a clear to transmit message, theclear to transmit message indicating a time when the thirdacknowledgment will be transmitted and a second different time when afourth acknowledgment will be transmitted to a fourth station;transmitting the clear to transmit message to the third station and thefourth station; and transmitting the third acknowledgment message to thethird station.
 28. The non-transitory computer-readable medium of claim27, wherein the first acknowledgment message is generated as a blockacknowledgment and the second acknowledgment message is generated as anacknowledgment of a single frame.
 29. The non-transitorycomputer-readable medium of claim 27, wherein the first acknowledgmentmessage is generated as a block acknowledgment and the secondacknowledgment message is generated as a block acknowledgment.